Many drugs are now available to be used in the treatment of cancer. However, in many cases the cancer either fails to respond to the anti-cancer therapy or its growth and spread is only slowed. Thus, there is still a need for new anti-cancer agents.
Even when a tumor initially responds to an anti-cancer therapy by decreasing in size or even going into remission, the tumor often develops resistance to the drug. Drug resistant tumors are characterized by a resumption of their growth and/or reappearance after having seemingly gone into remission, despite the administration of increased dosages of the anti-cancer drug.
For this reason, oncologists often administer combinations of anti-cancer drugs to a patient. Cancerous tumors are less likely to develop resistance when confronted with a multitude of different drugs, each having a different mode of action. Unfortunately, however, many tumors develop resistance, even when treated simultaneously with a number of different anti-cancer drugs. Cancers which reach this stage are referred to as “multi-drug resistant cancers”, or simply “MDR cancers”. There is little that can be done to halt or retard further progression of the disease, once a patient's cancer has become multi-drug resistant. Thus, there is an urgent need for new drugs which can be used to treat multi-drug resistant cancers.